No std value selected in block's radio field

I have a problem with setting default value on radio field with MB Blocks.

The field declaration seems to be OK:

[
    'name'    => esc_html__( 'Choose type', 'my-mb' ),
    'id'      => 'resource-type',
    'type'    => 'radio',
    'options' => [
        'link'       => esc_html__( 'Link', 'my-mb' ),
        'attachment' => esc_html__( 'Attachment', 'my-mb' ),
    ],
    'std'    => 'link',
],

Unfortunately, no option is chosen when I insert the block (also in new post).